Increased fetal hemoglobin (HbF) in cells of patients with beta hemoglobinopathies (thalassemia and sickle cell anemia) ameliorates the clinical symptoms of the underlying disease. Recently, several pharmacologic agents have been used to stimulate HbF synthesis; treatment of patients with 5-azacytidine or hydroxyurea resulted in higher HbF levels; yet, the clinical benefit is still unclear. Since these agents are either toxic and/or have been implicated in carcinogenesis, there is a considerable interest in other, less toxic agents with the potential to increase HbF. So far only a handful of agents have been tested, mainly due to the lack of an appropriate experimental system that allows a rapid and accurate determination of the effect on relevant cells. We have recently developed a novel, two phase liquid culture system for growing erythroid progenitors derived from the peripheral blood of normal individuals and patients with hemoglobinopathies. We showed that the system recapitulates many hematological effects of hydroxyurea in vivo, including stimulation of HbF production. The purpose of our research is to utilize this procedure and modified methods for quantitation of hemoglobins developed by uss to study the regulation of Hb production and to screen agents for their HbF-stimulating potential with the final objective to produce an efficient, low toxicity therapy. The experiments include optimization of the conditions for stimulation of HbF production, followed by screening of various agents (including derivatives of hydroxyurea, phenyl-fatty acids, erythropoietin, hemin) and subsequently studying their mode(s) of action. The latter studies will provide the rationale for further screening of additional agents and for their chemical modification in order to increase efficacy. Classification of the drugs according to functional and mechanistic considerations will enhance experiments with combination of drugs belonging to different groups and, thus, expected to act synergistically. In addition, we are attempting to develop, based on the cell culture system, as assay for e valuating an individual patient's response to a particular drug or drug combination. This will prevent both expensive and potentially risky treatment from patients which do no respond and suggest an alternative treatment (e.g. by other agents).